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United States Patent | 6,134,321 |
Pitsch | October 17, 2000 |
A telephone line monitoring circuit uses an optoisolator to convert the telephone line current to a voltage which is applied to the input of an AID converter. The A/D values are coarse values representing telephone line current. The A/D is sampled at a predetermined interval to identify changes introduced by the telephone company central office, and to take those changes into account when deciding if an extension telephone has gone off-hook. When a customer causes an extension telephone to go off-hook, the line current divides between the extension telephone and the IRD modem, and such change is detected.
Inventors: | Pitsch; Robert Alan (Carmel, IN) |
Assignee: | Thomas Licensing S.A. (Boulogne, FR) |
Appl. No.: | 091314 |
Filed: | June 16, 1998 |
PCT Filed: | December 18, 1996 |
PCT NO: | PCT/US96/20117 |
371 Date: | June 16, 1998 |
102(e) Date: | June 16, 1998 |
PCT PUB.NO.: | WO97/23985 |
PCT PUB. Date: | July 3, 1997 |
Jan 02, 1996[GB] | 9600002 | |
Jun 28, 1996[GB] | 9613608 |
Current U.S. Class: | 379/399.01; 379/106.08; 379/443; 379/902 |
Intern'l Class: | H04M 011/06 |
Field of Search: | 379/399,22,23,412,418,106.08,161,377,443,442,902,93.05,93.28 |
4203006 | May., 1980 | Mascia | 379/443. |
4807278 | Feb., 1989 | Ross | 379/184. |
4958371 | Sep., 1990 | Damoci et al. | 379/377. |
5291545 | Mar., 1994 | Stahl | 379/98. |
5422939 | Jun., 1995 | Kramet et al. | 379/106. |
5444772 | Aug., 1995 | Coker | 379/161. |
5809109 | Sep., 1998 | Moyal et al. | 379/22. |
Foreign Patent Documents | |||
338654 | ., 0000 | EP. | |
95/14344 | ., 0000 | WO. |